Pressure-volume-temperature dependence of poly-ε-caprolactam/clay nanocomposites

The pressure-volume-temperature (PVT) dependence of commercial poly-epsilon-caprolactain melt (PA-6) and based on it a nanocomposite containing 1.6 wt % of exfoliated montmorillonite (PNC) as well as their 1: 1 mixture was determined at T = 300-560 K and P = 0-150 MPa. Incorporation of clay into PA-6 resulted in lowering the specific volume of PNC by about 1.0%. For all three molten resins excellent agreement between experiment and the results from Simha-Somcynsky lattice-hole theory was found. The hole (free volume) fraction, a sensitive indicator of structural changes, shows a pressure-dependent reduction of ca. 14-15% in PNC as compared with the neat PA-6. An evaluation of the binary interactions from the computed mean scaling parameters of the theory requires definition of the constituents. On the basis of experimental and computer simulation results in the literature, the following model was adopted: Flat disk particles of specified diameter are covered with a uniform layer of solidified PA-6 of specified thickness, thus forming hairy clay platelets (HCP). The remainder of PA-6 constitutes the matrix. Its mobility and other properties vary with the distance from the clay surface in the normal direction and reach as an asymptotic limit bulk values. Thus, the characteristic interaction parameters of the matrix vary with the interparticle distance and hence with clay content. The estimated cross-interaction parameters are appropriate averages of the two self-interaction quantities.